Apheresis is a procedure in which individual blood components are collected and separated from whole blood that is temporarily withdrawn from a donor. Typically, whole blood is withdrawn through a needle inserted into a vein of a donor's arm; anticoagulant is added to the blood, and it is pumped into a separator such as a centrifugal bowl. Once the whole blood is separated into its various components based on physical characteristics such as density (e.g., red blood cells, white blood cells, platelets, and plasma), one or more of the components can be removed from the centrifugal bowl. The remaining components can be returned to the donor, in some cases with optional compensation fluid to make up for the volume of the removed component or to facilitate transit. The compensation fluid is often saline. The process of drawing whole blood and returning the separated components to the donor continues until the quantity of the desired component has been collected, at which point the process is stopped. A central feature of apheresis systems is that the processed but unwanted components are returned to the donor. Separated blood components may include, for example, a high-density component such as red blood cells, an intermediate-density component such as white blood cells or platelets, or a low-density component such as plasma.
Blood processing systems, such as apheresis systems, typically add an anticoagulant (e.g., sodium citrate/citric acid in saline or dextrose solution) to prevent blood or blood components from clumping and coagulating during collection within the blood collection system or in the collected components. Typically, the anticoagulant is directly mixed with the whole blood as it is drawn from the donor. The ratio of anticoagulant to whole blood may be set to a specific ratio. The U.S. FDA has established particular ratios of anticoagulant to whole blood when collecting source plasma. See, e.g., Kathryn C. Zoon, Director, FDA Center for Biologies Evaluation and Research, Volume Limits for Automated Collection of Source Plasma (Nov. 4, 1992); and see Compliance Policy Guide 252.110 Volume Limits for Automated Collection of Source Plasma (Mar. 6, 2000) (hereafter collectively referred to as “FDA Volume limits”; shown in Table 1, below).
An additional concern is the amount of anticoagulant added to collected components beyond the intended ratio to whole blood. Any additional anticoagulant dilutes the concentration of the collected components in the volume of the fraction (e.g., plasma). This additional volume can complicate or reduce the efficiency of downstream processing of various blood components, particularly plasma. Accordingly, it is desirable to limit any excess in the amount of anticoagulant added to the collected blood components.
A further reason for limiting the amount of anticoagulant added to blood is that the quantity (volume) of the blood component collected from the donor is typically determined by the weight of the collected anticoagulated sample. This weight often includes the anticoagulant used to prime the lines prior to commencing blood collection from the donor. This additional mass contributed by the priming anticoagulant contributes to the apparent mass of the collected blood component. As such, the quantity of the collected blood component is reduced because of the mass of priming anticoagulant. While the difference in mass contributed by the priming anticoagulant in the lines prior to collection may be negligible for a single donation and not of clinical significance to the donor, a consistent mass difference compounds when accumulated over many such donations. Thus, the quantity of blood component(s) that are not collected because of priming anticoagulant becomes significant over numerous collections, such as for commercial-scale preparation of blood components. Described herein are methods for remediating the priming anticoagulant weight contribution by aligning the anticoagulant within the blood collection device so that a reduced volume of pure anticoagulant is directed to the separation system preceding the flow of anticoagulated blood, upon commencing blood collection.